The primary objective is to evaluate the effects of NVP versus placebo (administered to HIV-infected women in labor and to the infant within the first 48-72 hours of life) on the incidence of HIV transmission. The secondary objectives are: 1) to evaluate the safety and tolerance of oral NVP in pregnant HIV-infected women and in HIV-exposed infants; 2) to determine NVP pharmacokinetic parametes in a large population of neonates; 3) to evaluate the relationship between NVP pharmacokinetic parameters and transmission; 4) to investigate the impact of maternal medications, such as protease inhibitors, on neonatal NVP pharmacokinetic parameters; 5) to evaluate the relationship between maternal viral load at delivery and HIV transmission in both the treatment and control groups; and 6) to determine the effect of nevirapine treatment on HIV RNA levels in infants who are determined to be HIV-infected.